Metallurgical processes such as basic oxygen steelmaking often employ large water-cooled oxygen lances (typically, about 8 inches to about 16 inches in diameter and approximately 65-85 feet long) to efficiently remove oxidizable elements from molten metal in a metallurgical converter. These lances, which typically weigh up to approximately 10 tons, are known as post-combustion lances. Typically, in addition to the primary oxygen ports at the tip of the lance, the prior art post-combustion lance includes a ring of small oxygen ports located on the outside of the lance a distance up the lance from the primary oxygen tip. The ring is known as a post-combustion (or “PC”) distributor.
Due to heat transfer requirements, and also to protect the PC distributor from the furnace atmosphere and the localized heat generated from the post-combustion reaction, the PC distributor (and often, the piping associated therewith) is made of high thermal conductivity metals such as high purity copper.
Although the post-combustion lance often is used to direct oxygen into a metallurgical converter, various other gases may be directed through the lance, depending on the reactions desired. Any and all reaction gases directed through the lance are generally referred to hereinafter as a “gas” for convenience, it being understood that the gas may be oxygen or any other reaction gas, or any mixture of any such gases. Typically, the gas is injected through the lance at very high rates. For example, oxygen may be injected into the lance at rates of between 300 cubic meters/min. and 600 cubic meters/min.
Cross-sections of a typical post-combustion lance 10 of the prior art are provided in FIGS. 1A and 1B.
The lance 10 extends between an upstream end 12, at which the gas is introduced therein, and a downstream end 14, at which a primary tip 16 is positioned. The introduction of the gas at the upstream end is represented by arrow “A” in FIG. 1A. A PC distributor 18 is positioned at a predetermined distance (designated “L” in FIG. 1A) from the end of the tip 16. The typical lance includes a lance body 20 having an upper portion 22 and a lower portion 24, being the outermost tube elements. The upper portion 22 typically has slightly larger inner and outer diameters than those of the lower portion 24 respectively. The body 20 includes the PC distributor 18, which is mounted between the upper and lower portions 22, 24, as shown in FIG. 1B. Typically, the upper and lower portions 22, 24 are substantially round in cross-section, i.e., they are generally cylindrical.
As shown in FIGS. 1A and 1B, the prior art post-combustion lance 10 typically (but not necessarily) also includes an upper inner tube 26 with an upstream first portion 28, a larger second portion 30, and a connecting portion 32 connecting the first and second portions 28, 30. Also, a lower inner tube 34 is positioned inside the body 20, downstream from the upper inner tube 26. Typically, the upper and lower inner tubes 26, 34 are positioned coaxial with each other and with the body 20. The upper and lower inner tubes 26, 34 are shaped to direct part of the gas to the PC distributor 18, and also to direct a part of the gas toward the lower inner tube 34, from which such part exits the lance at the tip 16. For example, the first part of the gas typically may be about ten percent of the gas flowing through the lance, with the second part being the balance. The part of the gas exiting the PC distributor is represented by arrows “B” in FIG. 1A, and the part of the gas exiting the tip 16 is represented by arrow “C” in FIG. 1A.
As is well known in the art, the upper and lower portions 22, 24 typically include cavities 25 through which water (not shown) is circulated while the post-combustion lance 10 is in use, to cool the lance body 20. Typically, the water is introduced at the upstream end 12 into an intake cavity which extends to the downstream end 14 and the primary tip 16, and the water returns to the upstream end 14 via an output cavity. The cavity 25 is at least partially defined by an upper intermediate element 29 in the upper portion 22 (FIG. 1B). In the lower portion 24, the cavity 25 is at least partially defined by a lower intermediate element 31.
As is also well known in the art, both the upper inner tube 26 and the lower inner tube 34 are secured to the body. The upper and lower portions 22, 24 are substantially cylindrical, and positioned substantially coaxial with each other. For instance, the axes defined by the upper and lower portions 22, 24 are identified by reference numeral 27 in FIG. 1B. In addition, the upper inner tube 26 typically is positioned substantially coaxial with the upper and lower portions 22, 24. Also, in the prior art lances in which the lower inner tube 34 is included, the lower inner tube 34 (which typically is substantially cylindrical) typically is positioned substantially coaxial with the upper and lower portions 22, 24 and with the upper inner tube 26. It will be understood that various prior art lances are known.
The lance is subjected to bending stresses during its service life, particularly during loading and unloading operations and during lance deskulling operations, where steel and slag buildup on the lance exterior surfaces 36 is removed using aggressive mechanical means, including, e.g., machinery employing hydraulic and/or pneumatic hammers and steel tips. When in use, the lance typically is supported only at the upper portion (i.e., above the distributor). Accordingly, the prior art lance typically is subject to deflection (i.e., substantially or at least partially transverse deflection) due to the bending stresses to which it is subjected. For example, the prior art lance 10 in FIG. 1B may be urged to deflect transversely (i.e., relative to the axis 27) by downward deflection of the lower portion relative to the upper portion, as indicated by arrow “D” in FIG. 1B.
Lances equipped with the PC distributor typically are prone to severe bending (i.e., deflection) and, in some cases, failure at the PC distributor, because of the relatively low yield strength of the high thermal conductivity components in the PC distributor. Since the introduction of the mid-lance PC distributor (i.e., at least in the 1980s, and possibly earlier), no effective solutions to the bending and/or failure problems have been implemented. Prior art post-combustion lances typically bend after a relatively short period in service, requiring relatively frequent replacement of the PC distributor.
Previous attempts to address this problem included the development of external removable protective sleeves which are put on new and refurbished PC distributor equipped lances to protect the lances during shipping to the user's facilities. However, the protective sleeves must be removed before the lance is put into service. In practice, sleeves are typically removed prior to completion of the unloading and installation of the lance. As a result, the lance is often bent subsequent to the protective sleeve removal, i.e., during the completion of installation, while in service, or while the lance is loaded back onto the truck for return repair at the end of its service life.
As is well known in the prior art, post-combustion lances may also include one or more spacers 21′, to maintain proper alignment of the tubes when the lance is being assembled. The spacers 21′ also serve to stiffen the lance to a small extent, however, it appears that they generally have only a limited, localized effect in this regard. For instance, another prior art post-combustion lance 10′ including spacers 21′ is illustrated in FIGS. 1C-1H. (The balance of the drawings disclose the invention herein.) The reference numerals relating to the prior art lance illustrated in FIGS. 1C-1H are designated by prime (′) symbols for the sake of convenience.
As can be seen, for example, in FIG. 1D, in the prior art, spacers 21′ are mounted on a lower intermediate element 31′. In general, the typical spacers 21′ are formed as elongate ridges on an outer surface of a tube element. The spacers 21′ preferably are relatively narrow (FIG. 1F), and spaced apart from each other around an outer surface 33′ of the lower intermediate element 31′ (FIG. 1F).
Additional spacers 21′ are shown in FIG. 1E. For instance, spacers 21A′, 21B′ are mounted on an upper inner tube 26′ (FIG. 1E). Additional spacers 21C′, 21D′ are positioned on a slip joint part 26A′ of the upper inner tube 26′ (FIG. 1E). Also, and as can be seen in FIG. 1E, spacers 21E′, 21F′ are mounted on an upper intermediate element 29′. The PC distributor 18′ is also illustrated in FIG. 1E, and additional spacers 21G′, 21H′, mounted on the lower intermediate element 31′, can also be seen in FIG. 1E.
FIG. 1E also shows that a first internal element 23′ of the PC distributor 18′ is welded to a lower inner tube 34′ and positioned adjacent to a second internal element 38′. As can be seen in FIG. 1E, the post-combustion lance 10′ also includes an o-ring gland 35′ mounted in the first internal element 23′, to enable movement of the first internal element 23′ and the second internal element 38′ relative to each other generally axially (i.e., in a direction substantially parallel to the axis 27′). As can be seen in FIG. 1E, the o-ring gland 35′ preferably includes a number of o-rings 37′. Those skilled in the art will appreciate that, in order for such movement to take place, a similar arrangement (i.e., an o-ring gland, to permit substantially axial relative movement of adjacent elements) is typically also included at the upper end of the upper portion 22′. This other o-ring gland or similar arrangement (not shown) typically is positioned near a manifold (not shown) through which oxygen (and other gases, as required) and water are provided to the lance. As is well known in the art, the o-ring glands are needed in order to permit expansion and/or contraction of various elements in the lance 10′, due to extreme temperature differences.
As noted above, because the PC distributor tends to be relatively weak (i.e., because it is primarily made of copper), the lance 10′ tends to bend at the distributor. In general, the lower portion 24′ tends to move downwardly (under the influence of gravity), in the direction indicated by arrow “J” in FIG. 1C. From FIGS. 1C and 1E, however, it can be seen that the o-ring gland 35′ also provides a relatively weaker area in the lance 10′, about which the lower portion 34′ tends to bend downwardly. In effect, the positioning of the o-ring gland 35′ in the PC distributor 18′ tends to undermine the overall structural integrity of the lance 10′.
For example, as can be seen in FIGS. 1F-1H, spacers 21J′ and 21K′ are positioned on an outer surface 39′ of the lower inner tube 34′. However, each of the spacers 21J′ and 21K′ has an outer region 41′ that faces an inner surface 43′ of the lower intermediate element 31′, i.e., the outer region 41′ is positioned opposite to the inner surface 43′. The outer region 41′ and the inner surface 43′ are separated by a gap 45′. Similarly, spacers 21L′ and 21M′ are mounted on the outer surface 33′ of the lower intermediate element 31′. Each of the spacers 21L′, 21M′ includes an outer region 47′ that faces an inner surface 49′ of an exterior tube 51′. In each case, the outer region 47′ is spaced apart from the inner surface 49′ by a gap 53′ (FIG. 1H).
It can be seen, therefore, that the spacers of the prior art generally do not provide sufficient support to the body, and that positioning one or more of the o-ring glands at or near the distributor tends to weaken the lance.